This invention relates, in general, to a mold assembly for encapsulating items, and more particularly, to the use of a resilient material in a mold assembly to compensate for dimensional variations of a cavity plate or the work piece itself.
In the manufacture of components it is often desirable to encapsulate these components with a protective material. This is particularly true of small components or work pieces such as semiconductor devices. In the past, an upper mold half and a lower mold half forming a plurality of cavities there between have been used. The semiconductor device is inserted in the cavity and then encapsulating material is injected into the cavity to encapsulate the semiconductor device. The mold plates are machined to very tight tolerances. However, it is more difficult to maintain the semiconductor devices to the same tight tolerances. This is particularly true for rectifier diodes packaged as button diodes. The mold cavity is machined to have one face-to-face dimension whereas the button diode face-to-face dimension actually varies in height and parallelism also. This will cause excess clearance for some products and interference fit with others resulting in product damage. A mold cavity having excess clearance will result in a thin layer of the encapsulating material being forced into the opening caused by the excess clearance resulting in what is commonly called flash. This flash was then removed in a subsequent operation which increased the cost of manufacturing the device and occasionally also resulted in damage to the device.
Accordingly, it is an object of the present invention to provide a mold assembly which uses a resilient material in order to compensate for dimensional variations of a device being encapsulated.
Another object of the present invention is to use a resilient material to compensate for dimensional variations of the mold plates themselves.
Yet another object of the present invention is to provide a method of encapsulating a work piece in a manner to eliminate flash.
Yet a further object of the present invention is to provide a method for encapsulating a semiconductor device wherein a sheet of resilient material is used to seal a portion of the mold cavity.